Proper tip = $3?? People have lots of ways to calculate the value of service. Looking at your method from another perspective -- you gave the server about 5%. So are you being clever or cheap? How well did the server take care of you during the meal? Granted, at the very end of the service, the server did a possibly boneheaded thing and gave you change that couldn't be used to make a tip in any common amount. However (1) there could be other reasons besides being a bonehead -- what if he's out of smaller bills, the bar can't help, and he can't find a manager, so he decides to get you the check because he's concerned you've already waited a while while he runs around looking for change? (2) that last interaction was only a small part of the service received.

If you'd like change in other denominations in order to give a tip in a certain amount, would you ever consider asking?